Electrical connection



June 7, i925',

P. ROBERG ELECTRICAL CONNECTION F'lled Aug 26 1921 Patented June 7,1927.

UNITED STATES PATENT OFFICE.

PHILIP ROBERG, OF ELMHURST, NEW YORK, ASSIGNOR, BY MESNE ASSIGNMENTS, TO

NATIONAL CARBON COMPANY, INC., 0F

Your.

NEW YORK, N. Y., A CORPORATION OF NEW' ELECTRICAL CONNECTION.

Application led August 26, 1921.

This invention relates to the attachment of electrical conductors tocurrent receiving members and has particular reference to improvementsin means and compositions for securing flexible cable connections to thecommutator brushes of dynamo-electric inachines.

Brushes of this type are as a rule subjected to substantially continuousvibration and it has proved diificult to connect a- Wire or cable tothem so that it Will not Work loose during service, resulting in anincrease of resistance and undue heating. Securing the cable by means ofbolts, rivets, or the like, materially complicates the manufacture ofthe brush. A simpler method Which has been proposed is to embed the endof the flexible connector in solder or other easily fusible alloy Suchconnections are not reliable, however, for the reason that brushes arelikely to be heated by the current to a temperature above the meltingpoint of the alloy The patent to H. B. Eynon, No. 1,188,635', dated June27, 1916, describes a carbon brush connection involving the use ofcopper amalgam as a cementing means for attaching the cable to thebrush. The `process outlined in this patent enables a relativelysatisfactory connection to be made in a very simple manner. I havediscovered, however, that by a modification of the composition of theamalgam and certain other procedures relating to its use, I secure aconnection of substantially diminished resistance during service andgreater strength.

`The present invention consists broadly in the use of carbon, preferablyin the form of graphite, with copper amalgam which may be of the typedescribed in the abovementioned patent to E on, or with any metallicpacking materlal suitable for securing acable to a brush,.for example,comvpacte copper powder The invention Will be described in detail -inconnection with the accompanying drawings, in which Fig. 1 is. avertical section through a brush carryin' a cable attached accordin to apreferre form of my invention, an,

Figs. Zand 3 are vertical sections through brushes showing modifiedforms of hold- 1n means.

vferring tothe drawings, the flexible Serial No. 495,499.

type of conductor may be used. rlhe brush 2 may consist of any suitablecomposition of comminuted carbon held together by a binder and maycontain graphite, copper or other electrically conductive materials. Theinvention is not limited to any particular form of brush cavity designedto receive the end of the cable. lThe connection may advantageously bemade by drilling a straight cylindrical hole of Asuitable diameterthrough the top of the brush, and of a depth depending on the size ofthe brush. The end of cable l is inserted centrally in the' drilled holeand the connection is completed by filling the cavity about the cableWith a carbon-containing compactible metallic substance, which serves asa composite electrical and mechanical bond holding the cable securely inthe brush. Electroplating of the hole is not essential to the successfuluse of my invention, but it may be employed.

Various amalgams, or metals in the form of compactible powders orfilaments, can be used, but a copper or copper; bronze amalgam ispreferred. The amount of graphite mixed With the metalor amalgam may beadjusted so as to obtain a connection of the desired type. For example,in cases Where an especially high pull out resistance is not demanded,the graphite content may advantageously be around 10%. This proportionof graphite in the metallic packing insures a continuous loW resistanceconnection throughout the service of the brush, and the stren th of theconnection is substantially equa to those made with metal alone. Tampingof the bonding mixture into the brush opening is considerablyfacilitated by the presence of such relatively large amounts ofgraphite. The strength of the bond is somewhat greater, however, Whenlower percentages of graphite are used. I have found that the admixtureof about 21/2% of graphite in general gives .a maximum with lrespect toboth strength and conductivity during service. The stated percentagesare, of course, illus trative only, and may be varied in accordance withthe particular character of connection desired.

A typical eementing amalgam may be preparedby mixing 100 parts by weightof copper or copper bronze powder and parts of mercury, stirring withdilute sulfurie acid to a pasty consistency and rubbing the mixturethoroughly until amalgamation is complete, after which the acid isremoved by washing. At this stage the amalgam is porous and plastic, and3 parts by Weight of graphite are' added with thorough mixing. WVhentampedinto the brush cavity, this forms a coherent mass or plug of hi helectrical conductivity between the eagle and the carbon or itselectroplated surface.

The amalgam described expands to an extent sufficient to bind the cablefirmly in the brush cavity. In addition, a superficial amalgamation ofthe strands of the conductor and the copper plating occurs, tending alsoto hold the parts together by the merging of the 'amalgam lling into themetalsA v adjacent it.

. coatin Instead of incorporating the graphite in the amalgam, a coating5 of graphite may be applied to the cavities, which need not beelectro-plated, as shown in Fig. 2. This may be advantageously appliedby f swabbing the Walls of the cavities with aphite. The thickness .ofthe coating ma varied, but a relatively thin layer is pre erable andsubstantially prevents the formation of a high resistance contact, whichis likely to -occur when copper amalgam containing no graphite isapplied directly to the surface of the brush cavity.' When the graphitecoating is applied, the amalgam need not contain carbon, but thegraphitecopper amalgam above described, or others of its type, may ofcourse be used if desired.

In the form of nay-invention illustrated in Fig. 3, a layer v6 ofgraphite is tamped about the' 'lower end of the flexible con-v ductor.Any suitableconductive bonding material 7, which may advantageously bea. metal or amalgam packing, is placed above layer 6. The acking maycontain graphite as described a ove, butin general this will be omittedas the primary purpose of the metal or amalgam is to make a bond ofadequate strength between the brush'and thel conductor. The -use of thegraphite layer ensuresa continuous low reslstance contact duringservice.

My invention consists broadly in the formation of a ,compositeelectrical and mechanical bond between carbon brushes and conductors bythe joint use of graphite and a conductive bondm material, especially ametallic packing. arious s cific embodiments of this general idea, ot erthan those herein described, are within the scope of the ap nded claims.

claim:

11' The mm1-imm vif@ electric brush having a cavity therein, a conductorextend- 1 ing into said cavity and a composite electrical and mechanicalbond between vthe brush and the conductor, said bond including a metaland graphite.

2. The combination of an electric brush i having a cavity therein, aconductor extending into said cavity, a metal-containing plug forsecuring the conductor in the cavity, and graphite associated with saidplug to reduce the electrical resistance between 1 the conductor and thebrush during service.

3. 'Ihe combination of a carbon brush havin a cavity therein, acarbon-containing metal ic plug in said'cavit and a conductor secured41n good electrica connection with l the brush by the metallic plug. y

4. The combination of a carbon brush having a cavity therein, anelectro-plated lining for said cavity, a conductor projecting into saidcavity and a carbon-containin 1 amalgam plug establishing good electricand mechanical connection between said conductor and carbon.

5. The combination with an electric brush having a cavity therein, of aconductor having an end inserted in said cavity, said end bemg'embeddedin a layer of graphite and a layer of a metallic bonding substance.

6. The combination wit-h an electric brush having a cavity therein, of aconductor inserted in said cavity, a layer of graphite establishingelectrical connection between the lower portion of the conductor and thebrush, and `a conductive bonding material above said graphite layer.

7. The invention according to claim 6, in which the bonding material 1sa compactlble amalgam.

.opening in the brush.

9. In combination, an electric brush having an opening, a conductorhaving a rtion extending into said'opening, an an amalgam-gra hite bondin said opening for retaining sai portion of said conductor in saidopening.

l0. vThe invention according to claim 9, wherein the graphite content ofsaid bond is relatively low.

11. The invention according to'claim 9, wherein the Graphite content ofsaid bond is not greater than about 10% by weight, the remainder beingamalgam.

12. The invention according to claim 9 wherein the graphite content ofsaid bond is about 2.5% by weight, the remainder being an amalgamcomprising a mixture-of co per powder and meren?. l

In testimony whereof, aix my' ture.

.PrnLIP nonnen

